This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Specific Aims Specific Aim 1: Discovery of non-invasive urinary biomarkers for diagnosis of acute kidney transplant rejection (AR). To test the hypothesis that there are signature peptides and proteins which can serve as diagnostic protein/peptide biomarkers in urine of pediatric and adult patients with AR, compared to patients with stable graft function (STA), urinary proteins will be assayed by the use of LC-FTICR and validated by immunoassay (ELISA). Specific Aim 2: Identification of non-invasive urinary biomarkers for diagnosis of chronic allograft nephropathy (CAN) and calcineurin inhibitor nephrotoxicity (CNIT). Serially collected and clinically annotated urine specimens from renal transplant patients with stable graft (STA), CAN and CNIT, will be assayed by high sensitivity LC-MS and validated by immunoassay (ELISA). Specific Aim 3: Identification of protein and peptide signatures specific for invasive BK viral infection, specifically BK virus nephropathy (BKVJN) in kidney transplant patients. Mass spectrometric analysis of proteins and peptides will be conducted on three different sets of urine collected from renal transplant patients with (i) BK vyuria alone, (ii) BK vyuria and BK viremia, and (iii) BK vyuria, BK viremia and BKVN.